package com.wk.configs;

import com.alibaba.fastjson.serializer.SerializerFeature;
import com.alibaba.fastjson.support.config.FastJsonConfig;
import com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.MediaType;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

import java.util.ArrayList;
import java.util.List;

@Configuration
public class FastJsonConfiguration implements WebMvcConfigurer {

    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters)
    {
        /*
31         先把JackSon的消息转换器删除.
32         备注: (1)源码分析可知，返回json的过程为:
33                    Controller调用结束后返回一个数据对象，for循环遍历conventers，找到支持application/json的HttpMessageConverter，然后将返回的数据序列化成json。
34                    具体参考org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor的writeWithMessageConverters方法
35               (2)由于是list结构，我们添加的fastjson在最后。因此必须要将jackson的转换器删除，不然会先匹配上jackson，导致没使用fastjson
36        */
        for(int i=converters.size()-1;i>0;i--)
        {
            if(converters.get(i) instanceof MappingJackson2HttpMessageConverter)
            {
                converters.remove(i);
            }
        }
        FastJsonHttpMessageConverter fastJsonHttpMessageConverter = new FastJsonHttpMessageConverter();

        //自定义fastjson配置
        FastJsonConfig config = new FastJsonConfig();
        config.setSerializerFeatures(
                SerializerFeature.WriteMapNullValue,      //是否输出值为null的字段，默认false，我们打开它
                SerializerFeature.WriteNullListAsEmpty,   //将Collection类型字段的字段空值输出为[]
                SerializerFeature.WriteNullStringAsEmpty, //将字符串类型字段的空值输出为空字符串
                SerializerFeature.WriteDateUseDateFormat,
                SerializerFeature.DisableCircularReferenceDetect //禁止循环引用
        );
        fastJsonHttpMessageConverter.setFastJsonConfig(config);

        // 添加支持的MediaTypes;不添加时默认为*/*,也就是默认支持全部
        // 但是MappingJackson2HttpMessageConverter里面支持的MediaTypes为application/json
        // 参考它的做法, fastjson也只添加application/json的MediaType
        List<MediaType> fastMediaTypes = new ArrayList<>();
        fastMediaTypes.add(MediaType.APPLICATION_JSON_UTF8);
        fastJsonHttpMessageConverter.setSupportedMediaTypes(fastMediaTypes);
        converters.add(fastJsonHttpMessageConverter);

    }
}
